Flip chip bonding method and chip used therein

ABSTRACT

In a bonding process of a flip chip bonding method, a chip is bonded to contact pads of a substrate by composite bumps which each includes a raiser, a UBM layer and a bonding layer. Before the bonding process, the surface of the bonding layer facing toward the substrate is referred to as a surface to be bonded. During the bonding process, the surface to be bonded is boned to the contact pad and become a bonding surface on the contact pad. The bonding surface has an area greater than that of the surface to be bonded so as to reduce electrical impedance between the chip and the substrate.

FIELD OF THE INVENTION

This invention relates to a flip chip bonding method, and more particularly to a method of bonding a chip to a substrate using composite bumps.

BACKGROUND OF THE INVENTION

In a conventional flip-chip package 10 as shown in FIG. 1 , bumps 14 of a chip 13 are electrically connected to contact pads 16 of a substrate 15 by conductive particles 12 in an anisotropic conductive film (ACF) 11. The area of the conductive particles 12 contacting the bumps 14 and the contact pads 16 is small so as to increase electrical impedance between the chip 13 and the substrate 15 and lower effectiveness and reliability of the conventional flip-chip package 10.

SUMMARY

One object of the present invention is to provide a flip chip bonding method and a chip used therein, which is able to reduce electrical impedance between a chip and a substrate.

A flip chip bonding method of the present invention includes the steps of providing a substrate and a chip and performing a bonding process. The substrate includes contact pads, the chip includes a body, bond pads, a protective layer and composite bumps. The bond pads are arranged on the body, the protective layer covers a surface of the body and includes openings each exposes one of the bond pads. Each of the composite bumps is electrically connected to one of the bond pads and includes a raiser, a UBM layer and a bonding layer. The raiser is non-conductive and covered by the UBM layer, the UBM layer is electrically connected to the bond pads, the bonding layer covers the UBM layer and is electrically connected to the UBM layer, the bonding layer located over the raiser has a surface to be bonded which faces toward the substrate. During the bonding process, the composite bumps of the chip are bonded to the contact pads of the substrate, the surface to be bonded of the bonding layer of each of the composite bumps contacts one of the contact pads to become a bonding surface on each of the contact pads. The bonding surface has an area greater than that of the surface to be bonded.

A chip of the present invention includes a body, bond pads, a protective layer and composite bumps. The bond pads are arranged on the body, the protective layer covers a surface of the body and includes openings each exposing one of the bond pads, each of the composite bumps is electrically connected to one of the bond pads and includes a raiser, a UBM layer and a bonding layer. The raiser is non-conductive and covered by the UBM layer, the UBM layer is electrically connected to the bond pads, the bonding layer covers the UBM layer and is electrically connected to the UBM layer. The bonding layer is provided to be electrically connected to a contact pad of a substrate.

After bonding the composite bumps to the contact pads, the bonding surface of the bonding layer contacting the contact pads has an area greater than that of the surface to be bonded of the bonding layer, thus the bonding area of each of the composite bumps contacting each of the contact pads is increased to lower electrical impedance between the chip and the substrate and further ensure effectiveness and reliability of the flip-chip package.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view diagram illustrating a conventional flip-chip package.

FIG. 2 is a perspective diagram illustrating a chip in accordance with a first embodiment of the present invention.

FIG. 3A is a cross-section view diagram of FIG. 2 .

FIG. 3B is a cross-section view diagram along A-A line of FIG. 3A.

FIG. 4 is a cross-section view diagram illustrating a chip bonded to a substrate in accordance with a first embodiment of the present invention.

FIG. 5 is a cross-section view diagram illustrating a chip bonded to a substrate in accordance with a first embodiment of the present invention.

FIG. 6 is a perspective diagram illustrating a chip in accordance with a second embodiment of the present invention.

FIG. 7A is a cross-section view diagram of FIG. 6 .

FIG. 7B is a cross-section view diagram along A-A line of FIG. 7A.

FIG. 8 is a perspective diagram illustrating a chip in accordance with a third embodiment of the present invention.

FIG. 9A is a cross-section view diagram of FIG. 8 .

FIG. 9B is a cross-section view diagram along A-A line of FIG. 9A.

FIG. 10 is a perspective diagram illustrating a chip in accordance with one embodiment of the present invention.

FIG. 11 is a perspective diagram illustrating a chip in accordance with a fourth embodiment of the present invention.

FIG. 12A is a cross-section view diagram of FIG. 11 .

FIG. 12B is a cross-section view diagram along A-A line of FIG. 12A.

FIG. 13 is a perspective diagram illustrating a chip in accordance with a fifth embodiment of the present invention.

FIG. 14A is a cross-section view diagram of FIG. 13 .

FIG. 14B is a cross-section view diagram along A-A line of FIG. 14A.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIGS. 2 to 5 , a flip chip bonding method in accordance with a first embodiment of the present invention includes the steps of providing a chip 100, providing a substrate 200 and a bonding process. The substrate 200, which may be a glass substrate, can be provided before or after the step of providing the chip 100, and can be provided together with the chip 100. During the bonding process, the chip 100 is bonded to contact pads 210 of the substrate 200.

With reference to FIGS. 2 to 5 , the chip 100 includes a body 110, a plurality of bond pads 120, a protective layer 130 and a plurality of composite bumps 140. The bond pads 120 are arranged on the body 110, the protective layer 130 covers a surface 111 of the body 110 and includes a plurality of openings 131, each of the bond pads 120 is visible from one of the openings 131. In the first embodiment, each of the composite bumps 140 is a pyramid or cone extended in a direction Y vertical to the body 110.

With reference to FIGS. 2, 3A and 3B, each of the composite bumps 140 is electrically connected to one of the bond pads 120 and includes at least one raiser 141, a UBM (under bump metallization) layer 142 and a bonding layer 143. The raiser 141 is a nonconductive body which may be made of polymer material. In the first embodiment, each of the composite bumps 140 includes a plurality of raisers 141, each of the raisers 141 is a pyramid or cone extended in the direction Y and is located on the protective layer 130.

With reference to FIGS. 2, 3A and 3B, the UBM layer 142 covers the raisers 141 and is electrically connected to the bond pad 120. And preferably, the raisers 141 are fully covered by the UBM layer 142. The UBM layer 142 can be made of titanium (Ti), tungsten titanium (TiW), copper (Cu), nickel (Ni), gold (Au) or nickel vanadium (NiV).

The bonding layer 143 covers the UBM layer 142 and is electrically connected to the UBM layer 142. Preferably, the UBM layer 142 is fully covered by the bonding layer 143. The bonding layer 143 is provided to be electrically connected to the contact pad 210 of the substrate 200 and it can be made of gold (Au), copper (Cu), tin (Sn), gold/tin alloy (Au/Sn), tin-silver alloy (Sn/Ag), indium (In), bismuth/tin alloy (Bi/Sn) or tin/lead alloy (Sn/Pb). With reference to FIG. 4 , before the bonding process, the bonding layer 143 located over the raiser 141 has a surface to be bonded 143 a which faces toward the substrate 200.

With reference to FIG. 5 , the composite bumps 140 on the chip 100 are bonded to the contact pads 210 on the substrate 200 in the bonding process. Each of the composite bumps 140 contacts one of the contact pads 210 via the surface to be bonded 143 a of the bonding layer 143, and after the bonding process, the surface of the bonding layer 143 bonded to the contact pad 210 is referred to as a bonding surface 143 b. The bonding surface 143 b has an area greater than that of the surface to be bonded 143 a such that electrical impedance between the chip 100 and the substrate 200 can be reduced.

With reference to FIGS. 4 and 5 , in the first embodiment, a non-conductive film (NCF) 300 is provided between the substrate 200 and the chip 100 before the bonding process. And during the bonding process, the composite bumps 140 are provided to penetrate through the NCF 300 to allow the surface to be bonded 143 a of the bonding layer 143 to contact the contact pads 210, the substrate 200 and the chip 100 are compressed continuously to allow the surface of the bonding layer 143 facing toward the contact pad 210 to become the bonding surface 143 b and allow the NCF 300 to be filled between the substrate 200 and the chip 100 to cover the composite bumps 140.

A second embodiment of the present invention is shown in FIGS. 6, 7A and 7B. Different to the first embodiment, the raisers 141 of each of the composite bumps 140 are disposed on the bonding pad 120 in the second embodiment, thus each of the composite bumps 140 is protruded from the bond pad 120.

With reference to FIGS. 8, 9A and 9B, the raiser 141 of a third embodiment of the present invention is a rib-like raiser extended in a direction X substantially parallel to the surface 111 of the body 110. Along the direction X, each of the openings 131 of the protective layer 130 has a first width W1, and the raiser 141 has a second width W2 greater than or equal to the first width W1. The rib-like raiser 141 of the third embodiment can enhance compression strength of the chip 100 and distribute compressive stress in the chip 100 during the bonding process, so breaking of the chip 100 caused by stress concentration can be preventable.

With reference to FIGS. 8 . 9A and 9B, in the third embodiment, the UBM layer 142 located on the raiser 141 has a third width W3 along the direction X parallel to the surface 111 of the body 110, the third width W3 is less than or equal to the second width W2 of the raiser 141. In another embodiment as shown in FIG. 10 , the raiser 141 of one of the composite bumps 140 is connected to the raiser 141 of the adjacent composite bump 140 along the direction X, and the raisers 141 connected with each other become a raising strip formed as one piece.

In the third embodiment as shown in FIGS. 8, 9A and 9B, the bonding layer 143 located on the UBM layer 142 has a bonding rib 143 c which has a fourth width W4 along the direction X, the fourth width W4 is greater than or equal to the third width W3 of the UBM layer 142 located on the raiser 141. The bonding rib 143 c is electrically connected to the contact pad 210 and used to enhance bonding strength of the bonding layer 143 to the contact pad 210. Similarly, before the bonding process, the bonding rib 143 c has a surface to be bonded facing toward the substrate 200, the surface to be bonded of the bonding rib 143 c is used to contact the contact pad 210 during the bonding process and becomes a bonding surface of the bonding rib 143 c on the contact pad 210 after the bonding process. The area of the bonding surface is greater than that of the surface to be bonded such that the electrical impedance between the chip 100 and the substrate 200 can be reduced.

FIGS. 11, 12A and 12B show a fourth embodiment of the present invention. Different to the third embodiment, the rib-like raiser 141 of the fourth embodiment is disposed on the bond pad 120. The UBM layer 142 covers the raiser 141 and is electrically connected to the bond pad 120, the bonding layer 143 covers the UBM layer 142 and is electrically connected to the UBM layer 142. In the fourth embodiment, the raiser 141 is across the opening 131 as shown in FIG. 12B, and preferably, the raisers 141 of the adjacent composite bumps 140 are connected with each other and become a raising strip formed as one piece.

FIGS. 13, 14A and 14B represent a fifth embodiment of the present invention. Different to the third embodiment, the raiser 141 disposed on the protective layer 130 is extended toward the opening 131 of the protective layer 130 in the fifth embodiment, accordingly, the UBM layer 142 and the bonding layer 143 located on the raiser 141 are also extended toward the opening 131. The raiser 141 is fully covered by the UBM layer 142 located on the raiser 141, and the UBM layer 142 is fully covered by the bonding layer 143.

In the present invention, the raiser 141 of each of the composite bumps 140 is provided to distribute compressive stress in the chip 100 during the bonding process, and owing to the bonding surface 143 b of the bonding layer 143 located above the raiser 141, which contacts the contact pad 210, has an area greater than that of the surface to be bonded 143 a of the bonding layer 143 before the bonding process, the electrical impedance between the chip 100 and the substrate 200 can be reduced to ensure the effectiveness and reliability of the flip-chip package.

While this invention has been particularly illustrated and described in detail with respect to the preferred embodiments thereof, it will be clearly understood by those skilled in the art that is not limited to the specific features shown and described and various modified and changed in form and details may be made without departing from the scope of the claims. 

What is claimed is:
 1. A flip chip bonding method comprising the steps of: providing a substrate including a plurality of contact pads; providing a chip including a body, a plurality of bond pads, a protective layer and a plurality of composite bumps, the plurality of bond pads are disposed on the body, the protective layer is configured to cover a surface of the body and includes a plurality of openings, each of the plurality of openings is configured to expose one of the plurality of bond pads, each of the plurality of composite bumps is electrically connected to one of the plurality of bond pads and includes a raiser, a under metal metallization (UBM) layer and a bonding layer, the raiser is non-conductive and covered by the UBM layer, the UBM layer is electrically connected to the plurality of bond pads and covered by the bonding layer, the bonding layer is electrically connected to the UBM layer, the bonding layer located above the raiser has a surface to be bonded which faces toward the substrate; and performing a bonding process, the plurality of composite bumps of the chip are bonded to the plurality of contact pads of the substrate, the surface to be bonded of the bonding layer of each of the plurality of composite bumps is configured to contact one of the plurality of contact pads such that the bonding layer has a bonding surface on each of the plurality of contact pads, and an area of the bonding surface is greater than an area of the surface to be bonded.
 2. The flip chip bonding method in accordance with claim 1, wherein a non-conductive film (NCF) is provided between the substrate and the chip before the bonding process, the plurality of composite bumps are configured to penetrate through the NCF to allow the surface to be bonded of the bonding layer to contact the plurality of contact pads during the bonding process, the substrate and the chip are configured to be compressed continuously during the bonding process to allow the NCF to be filled between the substrate and the chip and cover the plurality of composite bumps.
 3. The flip chip bonding method in accordance with claim 1, wherein the raiser of each of the plurality of composite bumps is disposed on the protective layer or one of the plurality of bond pads.
 4. The flip chip bonding method in accordance with claim 3, wherein the raiser and the plurality of composite bumps are pyramids or cones extended in a direction vertical to the body.
 5. The flip chip bonding method in accordance with claim 3, wherein the raiser is a rib extended in a direction parallel to the surface of the body, each of the plurality of openings has a first width and the raiser has a second width which is greater than or equal to the first width, the UBM layer located on the raiser has a third width which is less than or equal to the second width.
 6. The flip chip bonding method in accordance with claim 5, wherein a bonding rib is formed on the bonding layer located on the UBM layer and has a fourth width along the direction parallel to the surface of the body, the fourth width is greater than or equal to the third width of the UBM layer.
 7. The flip chip bonding method in accordance with claim 6, wherein the raiser of each of the plurality of composite bumps is connected to the raiser of the adjacent composite bump along the direction parallel to the surface of the body.
 8. The flip chip bonding method in accordance with claim 3, wherein the raiser of each of the plurality of composite bumps is a rib extended in a direction parallel to the surface of the body and is across one of the plurality of openings.
 9. The flip chip bonding method in accordance with claim 8, wherein the raiser of each of the plurality of composite bumps is connected to the raiser of the adjacent composite bump.
 10. The flip chip bonding method in accordance with claim 3, wherein the raiser disposed on the protective layer is extended toward one of the plurality of openings of the protective layer, and the UBM layer and the bonding layer located on the raiser are extended toward one of the plurality of openings, the raiser is fully covered by the UBM layer located on the raiser, and the UBM layer is fully covered by the bonding layer.
 11. A chip comprising: a body; a plurality of bond pads disposed on the body; a protective layer configured to cover a surface of the body and including a plurality of openings, each of the plurality of openings is configured to expose one of the plurality of bond pads; and a plurality of composite bumps each electrically connected to one of the plurality of bond pads and including a raiser, a under metal metallization (UBM) layer and a bonding layer, the raiser is non-conductive and covered by the UBM layer, the UBM layer is electrically connected to the plurality of bond pads and covered by the bonding layer, the bonding layer is electrically connected to the UBM layer and is configured to be electrically connected to a contact pad of a substrate.
 12. The chip in accordance with claim 11, wherein the raiser of each of the plurality of composite bumps is disposed on the protective layer or one of the plurality of bond pads.
 13. The chip in accordance with claim 12, wherein the raiser and the plurality of composite bumps are pyramids or cones extended in a direction vertical to the body, the raiser is fully covered by the UBM layer located on the raiser, and the UBM layer is fully covered by the bonding layer.
 14. The chip in accordance with claim 12, wherein the raiser is a rib extended in a direction parallel to the surface of the body, each of the plurality of openings has a first width and the raiser has a second width which is greater than or equal to the first width, the UBM layer located on the raiser has a third width which is less than or equal to the second width.
 15. The chip in accordance with claim 14, wherein a bonding rib is formed on the bonding layer located on the UBM layer and has a fourth width along the direction parallel to the surface of the body, the fourth width is greater than or equal to the third width of the UBM layer.
 16. The chip in accordance with claim 15, wherein the raiser of each of the plurality of composite bumps is connected to the raiser of the adjacent composite bump along the direction parallel to the surface of the body.
 17. The chip in accordance with claim 12, wherein the raiser of each of the plurality of composite bumps is a rib extended in a direction parallel to the surface of the body and is across one of the plurality of openings.
 18. The chip in accordance with claim 17, wherein the raiser of each of the plurality of composite bumps is connected to the raiser of the adjacent composite bump.
 19. The chip in accordance with claim 12, wherein the raiser disposed on the protective layer is extended toward one of the plurality of openings of the protective layer, and the UBM layer and the bonding layer located on the raiser are extended toward one of the plurality of openings, the raiser is fully covered by the UBM layer located on the raiser, and the UBM layer is fully covered by the bonding layer. 